Photopolymerizable epoxy-containing compositions

ABSTRACT

Photopolymerizable epoxy compositions which comprise an epoxy-containing material and photosensitive aromatic iondonium salt of a halogen-containing complex ion are described as are coated substrates and methods for bonding materials together using such compositions.

This is a continuation of application Ser. No. 467,899 filed May 8,1974, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to photopolymerizable compositions. Moreparticularly, this invention relates to compositions which comprise anepoxy-containing material and an aromatic iodonium complex salt asphotoinitiator and which can be cured by exposure to actinic radiation.

2. Description of the Prior Art

Although photopolymerizable epoxy compositions comprising epoxy resinmaterials and photosensitizers have been desired for some time, thosewhich have previously been proposed suffer from one or more drawbacks.Thus, in U.S. Pat. No. 3,074,869 there are disclosed photosensitiveepoxy compositions containing a nitrosoamine as photosensitizer.Compositions of this type require relatively long exposure to a highintensity light source to produce complete polymerization. In U.S. Pat.Nos. 3,205,157 and 3,708,296, there are disclosed photosensitive epoxycompositions containing respectively aryldiazonium salts andaryldiazonium salts of halogen-containing complex anions. Suchcompositions have limited usefulness because they have poor thermalstability, because their spectral response is limited to the ultravioletregion of the spectrum, and because nitrogen is evolved duringphotopolymerization causing pinholes and bubbles in heavy coatings ofthe composition. In U.S. Pat. No. 3,450,613 there is described anotherphotopolymerizable epoxy composition comprising the reaction product ofan epoxy resin prepolymer and an ethylenically unsaturated organic acid,a photosensitizer, and optionally polyfunctional acids or bases. Thiscomposition on exposure to ultraviolet light gels by reason of thephotoinduced polymerization of the ethylenically unsaturated portion ofthe reaction product. Completion of the cure of the composition iseffected by heating to bring about reaction of the epoxy resin portionof the composition. Such compositions as this have limited usefulnessbecause of the requirement of both light and heat to effect completepolymerization of the composition. The composition furthermore is oxygensensitive and has poor thermal stability.

The present invention provides novel photopolymerizable compositions,comprising epoxy-containing materials and a photoinitiator, which aresensitive throughout the ultraviolet and visible spectral regions, i.e.,wavelengths from about 300 to 700 millimicrons and which may bephotocured by exposure for relatively short periods of time to radiationwithin this range of wavelengths.

SUMMARY OF THE INVENTION

In accordance with the present invention there are providedphotopolymerizable epoxy compositions which are readily photocured byexposure to actinic radiation comprising an organic compound having anepoxy functionality of at least 1 and certain photosensitive aromaticiodonium complex salts as photoinitiator and, optionally, a sensitizerfor said photoinitiator. The photopolymerizable epoxy compositions ofthe invention are sensitive throughout the ultraviolet and visiblespectral regions and photocure rapidly, without use of heat, to epoxypolymers which possess inherent superior toughness; abrasion resistance;adhesion to metal, glass, plastic, wood and other surfaces; andresistance to chemical attack. The aromatic iodonium complex saltphotoinitiator suitable for use in the compositions of the invention canbe defined by the formula ##STR1## wherein Ar¹ and Ar² are the same ordifferent aromatic groups known in the art and Z is an oxygen atom, acarbon-to-carbon bond joining Ar¹ and Ar², or ##STR2## where R₁ and R₂are selected from the group consisting of hydrogen, an alkyl radicalhaving 1 to 4 carbon atoms, and an alkenyl radical having 2 to 4 carbonatoms, and n is zero or 1; X⁻ is a halogen-containing complex anionselected from the group consisting of tetrafluoroborate,hexafluorophosphate, hexafluoroarsenate, hexachlorostannate,hexafluorostannate, hexachloroantimonate, and hexafluoroantimonate.

The aromatic iodonium cations are stable and are well known andrecognized in the art. See, for example, U.S. Pat. Nos. 3,565,906;3,712,920; 3,759,989; and 3,763,187; F. Beringer, et al., DiaryliodoniumSalts IX, J. Am. Chem. Soc. 81, 342-51 (1959) and F. Beringer, et al.,Diaryliodonium Salts XXIII, J. Chem. Soc. 1964, 442-51.

Representative Ar¹ and Ar² groups are aromatic groups having 4 to 20carbon atoms selected from phenyl, thienyl, and furanyl groups. Thesearomatic groups may optionally have one or more fused benzo rings (e.g.,naphthyl and the like; benzothienyl, dibenzothienyl; benzofuranyl,dibenzofuranyl; etc.). Such aromatic groups may also be substituted, ifdesired, by one or more of the following groups: halogen, nitro,hydroxyl, carboxyl, anilino or N-alkylanilino groups, ester groups(e.g., alkoxycarboxyl such as methoxycarbonyl and ethoxycarbonyl,phenoxycarbonyl), sulfo ester groups (e.g., alkoxysulfonyl such asmethoxysulfonyl and butoxysulfonyl, phenoxysulfonyl, and the like),amido groups (e.g., acetamido, butyramido, ethylsulfonamido, and thelike), carbamyl groups (e.g., carbamyl, N-alkylcarbamyl,N-phenylcarbamyl, and the like), sulfamyl groups (e.g., sulfamyl,N-alkylsulfamyl, N,N-dialkylsulfamyl, N-phenylsulfamyl, and the like),alkoxy groups (e.g., methoxy, ethoxy, butoxy, and the like), aryl groups(e.g., phenyl), alkyl groups (e.g., methyl, ethyl, butyl, and the like),aryloxy groups (e.g., phenoxy), alkylsulfonyl (e.g., methylsulfonyl,ethylsulfonyl, and the like), arylsulfonyl groups (e.g., phenylsulfonylgroups), perfluoroalkyl groups (e.g., trifluoromethyl, perfluoroethyl,and the like), and perfluoroalkylsulfonyl groups (e.g.,trifluoromethylsulfonyl, perfluorobutylsulfonyl, and the like).

Suitable examples of the aromatic iodonium complex salt photoinitiatorsinclude:

diphenyliodonium tetrafluoroborate

di(4-methylphenyl)iodonium tetrafluoroborate

phenyl-4-methylphenyliodonium tetrafluoroborate

di(4-heptylphenyl)iodonium tetrafluoroborate

di(3-nitrophenyl)iodonium hexafluorophosphate

di(4-chlorophenyl)iodonium hexafluorophosphate

di(naphthyl)iodonium tetrafluoroborate

di(4-trifluoromethylphenyl)iodonium tetrafluoroborate

diphenyliodonium hexafluorophosphate

di(4-methylphenyl)iodonium hexafluorophosphate

diphenyliodonium hexafluoroarsenate

di(4-phenoxyphenyl)iodonium tetrafluoroborate

diphenyliodonium hexachlorostannate

phenyl-2-thienyliodonium hexafluorophosphate

diphenyliodonium hexafluorostannate

diphenyliodonium hexachloroantimonate

diphenyliodonium hexafluoroantimonate

2,2'-diphenyliodonium tetrafluoroborate

di(2,4-dichlorophenyl)iodonium hexafluorophosphate

di(4-bromophenyl)iodonium hexafluorophosphate

di(4-methoxyphenyl)iodonium hexafluorophosphate

di(3-carboxyphenyl)iodonium hexafluorophosphate

di(3-methoxycarbonylphenyl)iodonium hexafluorophosphate

di(3-methoxysulfonylphenyl)iodonium hexafluorophosphate

di(4-acetamidophenyl)iodonium hexafluorophosphate

di(2-benzothienyl)iodonium hexafluorophosphate.

Of the aromatic iodonium complex salts which are suitable for use in thecompositions of the invention the preferred salts are the diaryliodoniumhexafluorophosphate such as diphenyliodonium hexafluorophosphate. Thesesalts are preferred because, in general, they are more soluble in inertorganic solvents than are other aromatic iodonium salts of complex ions.

The aromatic iodonium complex salts may be prepared by metathesis ofcorresponding aromatic iodonium simple salts (such as, for example, thediphenyliodonium bisulfate) in accordance with the teachings ofBeringer, et al., J. Am. Chem. Soc. 81, 342 (1959). Thus, for example,the complex salt diphenyliodonium tetrafluoroborate is prepared by theaddition at 60° C. of an aqueous solution containing 29.2 g. (150millimoles) silver fluoroborate, 2 g. fluoroboric acid, and 0.5 g.phosphorous acid in about 30 ml. of water to a solution of 44 g. (139millimoles) of diphenyliodonium chloride. The silver halide thatprecipitates is filtered off and the filtrate concentrated to yielddiphenyliodonium fluoroborate which may be purified byrecrystallization.

The aromatic iodonium simple salts may be prepared in accordance withBeringer et al., above, by various methods including (1) coupling of twoaromatic compounds with iodyl sulfate in sulfuric acid, (2) coupling oftwo aromatic compounds with an iodate in acetic acid-aceticanhydride-sulfuric acid, (3) coupling of two aromatic compounds with aniodine acylate in the presence of an acid, and (4) condensation of aniodoso compound, an iodoso diacetate, or an iodoxy compound with anotheraromatic compound in the presence of an acid. Diphenyliodonium bisulfateis prepared by method (3), for example, by the addition over a period ofeight hours at below 5° C. of a mixture of 35 ml. of conc. sulfuric acidand 50 ml. of acetic anhydride to a well-stirred mixture of 55.5 ml. ofbenzene, 50 ml. of acetic anhydride, and 53.5 g. of potassium iodate.The mixture is stirred for an additional four hours at 0°-5° C. and atroom temperature for 48 hours and treated with 300 ml. of diethyl ether.On concentrating, crude diphenyliodonium bisulfate precipitates. Ifdesired, it may be purified by recrystallization.

Epoxy-containing material useful in the compositions of the inventionare any organic compounds having an oxirane ring polymerizable by ringopening. Such materials, broadly called epoxides, include monomericepoxy compounds and epoxides of the polymeric type and can be aliphatic,cycloaliphatic, aromatic or heterocyclic. These materials generally haveat least one polymerizable epoxy group per molecule (preferably two ormore epoxy groups per molecule) and, in the polymeric type there aremany pendent epoxy groups (e.g., a glycidyl methacrylate polymer couldhave several thousand pendent epoxy groups per average molecularweight).

These epoxy-containing materials may vary from low molecular weightmonomeric materials to high molecular weight polymers and may varygreatly in the nature of their backbone and substituent groups. Forexample, the backbone may be of any type and substituent groups thereoncan be any group not having an active hydrogen atom which is reactivewith an oxirane ring. Illustrative of permissible substituent groupsinclude halogens, ester groups, ethers, sulfonate groups, siloxanegroups, nitro groups, amide groups, nitrile groups, phosphate groups,etc. The molecular weight of the epoxy-containing materials may varyfrom 58 to about 100,000 or more. Mixtures of various epoxy-containingmaterials can also be used in the compositions of this invention.

Such epoxy-containing materials are well known and include such epoxidesas epichlorohydrins, e.g., epichlorohydrin; alkylene oxides, e.g.,propylene oxide, styrene oxide; alkenyl oxides, e.g., butadiene oxide;glycidyl esters, e.g., ethyl glycidate, glycidyl-type epoxy resins,e.g., the diglycidyl ethers of Bisphenol A and of novolak resins, suchas described in "Handbook of Epoxy Resins" by Lee and Neville,McGraw-Hill Book Co., New York (1967).

Other useful epoxy-containing materials which can be used in thisinvention are those which contain one or more cyclohexene oxide groupssuch as the epoxycyclohexanecarboxylates, typified by3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate. For amore detailed list of useful epoxides of this nature, reference is madeto the U.S. Pat. No. 3,117,099, incorporated herein by reference.

Further epoxy-containing materials which are particularly useful in thepractice of this invention include glycidyl ether monomers of theformula ##STR3## where R is alkyl or aryl and n is an integer of 1 to 6.Examples are the glycidyl ethers of polyhydric phenols obtained byreacting a polyhydric phenol with an excess of chlorohydrin such asepichlorohydrin (e.g., the diglycidyl ether of 2,2-bis-(2,3-epoxypropoxyphenol)-propane). Further examples of epoxides of this type whichcan be used in the practice of this invention are described in U.S. Pat.No. 3,018,262, incorporated herein by reference.

There are a host of commercially available epoxy-containing materialswhich can be used in this invention. In particular, epoxides which arereadily available include propylene oxide, epichlorohydrin, styreneoxide, vinyl cyclohexene oxide, glycidol, glycidylmethacrylate,diglycidyl ether of Bisphenol A (e.g., those available under the tradedesignations "Epon 828" from Shell Chemical Co., "DER 331", "DER 332",and DER 334", from Dow Chemical Co.), vinylcyclohexene dioxide (e.g.,"ERL-4206" from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (e.g., "ERL4221" from Union Carbide Corp.),3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexenecarboxylate (e.g., "ERL-4201" from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate (e.g., "ERL-4289" fromUnion Carbide Corp.), bis(2,3-epoxy-cyclopentyl)ether (e.g., "ERL-0400"from Union Carbide Corp.), aliphatic epoxy modified with polypropyleneglycol (e.g., "ERL-4050" and "ERL-4052" from Union Carbide Corp.),dipentene dioxide (e.g., "ERL-4269" from Union Carbide Corp.),epoxidized polybutadiene (e.g., "Oxiron 2001" from FMC Corp.), siliconeresin containing epoxy functionality, flame retardant epoxy resins(e.g., "DER-580", a brominated bisphenol type epoxy resin available fromDow Chemical Co.), 1,4-butanediol diglycidyl ether (e.g., "AralditeRD-2" from Ciba-Geigy), polyglycidyl ether of phenolformaldehyde novolak(e.g., "DEN-431" and "DEN-438" from Dow Chemical Co.), and resorcinoldiglycidyl ether (e.g., "Kopoxite" from Koppers Company, Inc.).

Still other epoxy-containing materials are copolymers of acrylic acidesters of glycidol such as glycidylacrylate and glycidylmethacrylatewith one or more copolymerizable vinyl compounds. Examples of suchcopolymers are 1:1 styrene-glycidylmethacrylate, 1:1methylmethacrylate-glycidylacrylate and a 62.5:24:13.5methylmethacrylate-ethyl acrylate-glycidylmethacrylate.

Still other epoxy-containing materials are the polyurethane polyepoxideswhich are obtained by reacting an organic polyisocyanate with a triol ora mixture of a triol and diol to form an isocyanate terminatedpolyurethane prepolymer and reacting the prepolymer with a hydroxyaliphatic epoxide compound. Further examples of epoxy-containingmaterial of this type which can be used in the practice of thisinvention are described in U.S. Pat. No. 3,445,436, incorporated hereinby reference.

The photopolymerizable compositions of the invention comprisingepoxy-containing materials and aromatic iodonium complex saltphotoinitiators can be used as adhesives, caulking and sealingcompounds, casting and molding compounds, potting and encapsulatingcompounds, impregnating and coating compounds, etc., depending on theparticular epoxy materials and aromatic iodonium complex salt used. Thephotopolymerizable composition can be used as a one-componentcured-in-place composition. The photopolymerizable compositions areparticularly suitable in a variety of applications in the field ofgraphic arts due to their superior abrasion-resistance and adhesion torigid, resilient and flexible substrates such as metal, plastic, rubber,glass, paper, wood, and ceramics; their excellent resistance to mostsolvents and chemicals; and their capability of forming high resolutionimages. Among such uses are in making acid- and alkali-resist images forchemical milling, gravure images, offset plates, flexographic printing,screenless lithography, printing plates, stencil making, microimages forprinted circuitry, microimages for information storage, decorations ofpaper, glass, and metal surfaces, and light-cured coatings.

The photopolymerization of the compositions of the invention occurs onexposure of the compositions to any source of radiation emitting actinicradiation at a wavelength within the ultraviolet and visible spectralregions. Suitable sources of radiation include mercury, xenon, carbonarc and tungsten filament lamps, sunlight, etc. Exposures may be fromless than about 5 seconds to 10 minutes or more depending upon theamounts and particular epoxy materials and aromatic iodonium complexsalts being utilized and depending upon the radiation source anddistance from the source.

While not desiring to be bound by theory, the photopolymerizationapparently takes place by reason of the photoinduced degradation of thearomatic iodonium complex salt with the production of a Lewis acid whichcatalyzes the polymerization of the epoxy material. The curing is atriggered reaction, i.e., once the degradation of the aromatic iodoniumcomplex salt has been initiated by exposure to a radiation source, thecuring reaction proceeds and will continue even after the radiationsource is removed.

The aromatic iodonium complex salts useful in the photopolymerizableepoxy compositions of the invention are of themselves photosensitiveonly in the ultraviolet. They, however, are sensitized to the nearultraviolet and the visible range of the spectrum by sensitizers forknown photolyzable organic halogen compounds in accordance with theteachings of U.S. Pat. No. 3,729,313 which is incorporated herein byreference. Illustrative sensitizers are found in the followingcategories: aromatic amines, aminoketones, and colored aromaticpolycyclic hydrocarbons. The use of basic amino compounds is avoidedsince such compounds tend to inhibit the polymerization of the epoxymaterial.

The amount of aromatic iodonium complex salt that may be employed in thecompositions of the invention is from about 0.5 to 30 parts per 100parts of epoxy-containing material and preferably from about 2 to 7parts per 100 parts of epoxy-containing material. For those compositionswherein a sensitizer is used to make the composition sensitive toradiation in the visible range, about 0.01 to 1.0 parts and preferablyabout 0.1 to 1.0 parts by weight of sensitizer per part of aromaticiodonium complex salt may be employed.

The photopolymerizable compositions of the invention are prepared bysimply admixing, under "safe light" conditions, the aromatic iodoniumcomplex salt and the sensitizer, when used, with the epoxy-containingmaterial. Suitable inert solvents may be employed if desired wheneffecting this mixture. Examples of suitable solvents are acetone,acetonitrile, methanol and includes any solvent which does not reactappreciably with the epoxy-containing material, the aromatic iodoniumcomplex salt or the sensitizer. A liquid epoxy material may be used as asolvent for another liquid or solid epoxy material. A solvent, however,is generally used only to aid in providing a suitable viscosity to thecomposition for purposes of coating. Solventless compositions can beprepared by simply dissolving the aromatic iodonium complex salt andsensitizer in the epoxy-containing material with or without the use ofmild heating.

In the following examples which will serve to illustrate the presentinvention, all parts are parts by weight and all percentages are givenas percentages by weight, unless otherwise indicated.

EXAMPLES 1-6

In separate examples the various amounts of diphenyliodoniumhexafluorophosphate (designated φ₂ IPF₆) shown in Table I were added to5 parts of "DER-331" (a diglycidyl ether of Bisphenol A available fromDow Chemical Co. having an epoxy equivalency of about 190) and wellmixed at about 50° C. Each portion was then wire rod coated at 2.3 mils(0.006 cm.) thick onto a 2 mil (0.005 cm.) polyester film. Samples ofthe coating were then exposed to a 275 watt General Electric RS sunlampat a distance of 5 inches (12.7 cm.). The time required for the surfaceof the coating to become tack-free is listed in Table I.

                  TABLE I                                                         ______________________________________                                        Example   1       2      3      4    5      6                                 ______________________________________                                        φ.sub.2 IPF.sub.6 (Parts)                                                           0.05    0.10   0.15   0.20 0.25   0.30                              Tack-free                                                                     (Seconds) 120     90     80     60   25     25                                ______________________________________                                    

It may be observed by inspection of Table I that the time required forthe epoxy composition to become tack-free decreases from 120 seconds at1% concentration of diaryliodonium complex salt to 25 second at 5% ofthe salt. Increase of the salt concentration to 6% does not furtherdecrease the tack time because at 6%, the solubility of the salt in"DER-331" has been exceeded.

EXAMPLES 7-16

In separate examples, coatings were prepared as in Examples 1-6 fromphotopolymerizable compositions containing the various epoxy materialsand the various amounts of the various aromatic iodonium complex saltsshown in Table II, the coatings then being exposed to a General Electricsunlamp at 5 inches (12.7 cm.) or to a General Electric "H3T7" mercurylamp at 7 inches (17.8 cm.). The time required for the surface of thecoating to become tack-free is also reported in Table II.

                  TABLE II                                                        ______________________________________                                                                     Parts                                                                         By                                                                            Wt.         Tack-                                Ex-                          Com-  Expo- free                                 am-  Epoxy      Iodonium     plex  sure  Cure                                 ple  Material   Complex Salt Salt  Unit  (Sec.)                               ______________________________________                                         7   "DER-334"  φ.sub.2 IPF.sub.6.sup.(a)                                                              6     Sun-  25                                                                      lamp                                        8   "DER-334"  φ.sub.2 IBF.sub.4.sup.(b)                                                              6     H3T7  60                                    9   "DER-334"  φ.sub.2 IBF.sub.4                                                                      4     H3T7  90                                   10   "DER-334"  φ.sub.2 IPF.sub.6                                                                      2     H3T7  60                                   11   "ERL-4221" φ.sub.2 IPF.sub.6                                                                      4     H3T7  90                                   12   "ERL-4221" φ.sub.2 IBF.sub.4                                                                      4     H3T7  180                                  13   Phenyl     φ.sub.2 IPF.sub.6                                                                      4     H3T7  180                                       Glycidyl                                                                      Ether                                                                    14   "Epon-828" φ.sub.2 ISbF.sub.6.sup.(c)                                                             2     H3T7  60                                   15   "DER-331"  (CH.sub.3 - φ).sub.2 IPF.sub.6.sup.(d)                                                 6     Sun-  40                                                                      lamp                                       16   "Epon-828" φ.sub.2 ISbF.sub.6                                                                     5     Sun-  10                                                                      lamp                                       ______________________________________                                         .sup.(a) diphenyliodonium hexafluorophosphate                                 .sup.(b) diphenyliodonium tetrafluoroborate                                   .sup.(d) diphenyliodonium hexafluoroantimonate                                .sup.(d) ditolyliodonium hexafluorophosphate                             

EXAMPLES 17-23

Photopolymerizable compositions were prepared and coated as described inExamples 1-6 using the epoxy-containing materials, aromatic iodoniumcomplex salt, and sensitizing dye (wt. % based on wt. of complex salt)shown in Table III. The time required for the surface of the coating ofeach composition to become tack-free is presented in Table III.

                                      TABLE III                                   __________________________________________________________________________                                                             Tack-                                                                         free                      Epoxy                                          Exposure                                                                           Cure                 Example                                                                            Material                                                                             Complex Salt                                                                          Parts                                                                            (Wt. % Based on Wt. of Complex Salt)                                                                       Unit (Sec.)               __________________________________________________________________________    17   "DER-331".sup.a                                                                      (CH.sub.3φ).sub.2 IPF.sub.6                                                       (6)                                                                              2-Ethyl-9,10-di-          (10)                                                                             Sunlamp                                                                            10                                          methoxyanthracene                                      18   "DER-331".sup.a                                                                      (CH.sub.3φ).sub.2 IPF.sub.6                                                       (6)                                                                              Triphenylamine            (10)                                                                             Sunlamp                                                                            30                   19   "DER-331".sup.a                                                                      φ.sub.2 IPF.sub.6                                                                 (5)                                                                               ##STR4##                 (10)                                                                             Sunlamp                                                                            10                   20   "DER-331".sup.a                                                                      φ.sub.2 IPF.sub.6                                                                 (5)                                                                              5,10-Diethoxy-16,17-      (10)                                                                             H3T7 10                                          dimethoxyviolanthrene                                  21   "DER-331".sup.a                                                                      φ.sub.2 IPF.sub.6                                                                 (5)                                                                              Perylene                  (10)                                                                             H3T7 10                   22   "Epon 826".sup.b                                                                     φ.sub.2 ISbF.sub.6                                                                (5)                                                                              2-Ethyl-9,10-di-          (9)                                                                              Sunlamp                                                                             5                                          methoxyanthracene                                      23   "Epon 826".sup.b                                                                     φ.sub.2 ISbF.sub.6                                                                (5)                                                                              Same as for Ex. 19        (8)                                                                              Sunlamp                                                                             8                   __________________________________________________________________________     .sup.a Diglycidyl ether of Bisphenol A having epoxy equivalency of about      190.                                                                          .sup.b A low viscosity glycidyl ether of Bisphenol A with epoxyequivalenc     of about 185.                                                            

EXAMPLE 24

Solution of 20 grams "DER-331", 1.0 gram diphenyliodoniumhexafluorophosphate, and 0.1 gram 2-ethyl-9,10-dimethoxyanthracene wascoated at 30.0 mils (0.076 cm.) thick on 2 mil (0.005 cm.) thickpolyester film. After exposure of the coated film for 5 minutes at 5inches (12.7 cm.) from a General Electric sunlamp, a hard cured samplewas obtained, the coating being firmly bonded to the film. The curedsample was completely transparent and contained no bubbles. Unexposedportions of the coating can be washed away with acetone leaving a sharp,clearly defined image area.

EXAMPLE 25

A solution was prepared containing 5 grams of a 5% solution of a 1:1styrene-glycidylmethacrylate copolymer in acetone, 0.01 gram ofdiphenyliodonium hexafluorophosphate, and 0.005 grams2-ethyl-9,10-dimethoxyanthracene. It was coated on 2 mil (0.005 cm.)thick polyester film at a wet thickness of 2.3 mils (0.006 cm.) and airdried. A sample was exposed to a General Electric H3T7 lamp at 7 inches(17.8 cm.) distance through a √2 photographic step tablet for 3 minutesand dipped in acetone to remove the unexposed areas. Seven steps ofpolymerized material remained.

EXAMPLE 26

As another example of the utility of the compositions described herein aphotopolymerizable varnish is prepared which is useful for coatingfishing rod windings. The composition is prepared with the followingingredients:

    ______________________________________                                                              Parts                                                   ______________________________________                                        "DER-334" (a diglycidyl ether of                                              Bisphenol A)            100                                                   Phenyl glycidyl ether   10                                                    Diphenyliodonium hexafluorophosphate                                                                  2                                                     2-Ethyl-9,10-dimethoxyanthracene                                                                      0.1                                                   ______________________________________                                    

The "DER-334" and phenyl glycidyl ether are mixed with gentle heatingwhile the diphenyl iodonium complex salt and sensitizer are addedthereto with stirring. A clear photopolymerizable solution is obtained.

The photopolymerizable solution is coated onto the nylon thread windingsof a fishing rod guide. The thread had been previously heated to about50° C. so that the solution would saturate rapidly into the windingswhen applied thereto with a brush. The impregnated windings are thenexposed to a 275 watt sunlamp at a distance of about 7.5 centimeters forabout two minutes, the fishing rod being rotated slowly during exposure.After exposure in the manner described a second application ofphotopolymerizable solution to the windings is made, followed byexposure to a sunlamp to cure the coating. A smooth, varnished windingwith high gloss and durability is obtained.

This technique for coating windings on fishing rods is much faster andsimpler than with conventional techniques wherein solvent-based lacquersand varnishes are used.

I claim:
 1. A photopolymerizable composition comprising:(a) an organiccompound having an epoxy functionality of at least 1; (b) about 0.5 to30 parts by weight, per 100 parts by weight of said organic compound, ofan aromatic iodonium complex salt photoinitiator of the formula ##STR5##wherein Ar¹ and Ar² are aromatic groups having 4 to 20 carbon atoms andare selected from the group consisting of phenyl, thienyl, and furanylgroups; Z is an oxygen atom, a carbon-to-carbon bond, or ##STR6## whereR₁ and R₂ are selected from the group consisting of hydrogen, an alkylradical having 1 to 4 carbon atoms, and an alkenyl radical having 2 to 4carbon atoms, and n is zero or 1; and X⁻ is a halogen-containing complexanion selected from the group consisting of tetrafluoroborate,hexafluorophosphate, hexafluoroarsenate, hexachloroantimonate, andhexafluoroantimonate; and (c) about 0.01 to 1 part by weight ofsensitizing dye per part by weight of photoinitiator.
 2. Aphotopolymerizable composition in accordance with claim 1, wherein saidorganic material is selected from the group consisting ofepichlorohydrins, alkylene oxides, alkenyl oxides, glycidyl esters,glycidyl ethers, epoxy novolaks, copolymers of acrylic acid esters ofglycidol and copolymerizable vinyl compounds, and polyurethanepolyepoxides.
 3. A photopolymerizable composition in accordance withclaim 1, wherein said organic material comprises glycidyl ether of theformula ##STR7## where R is alkyl or aryl and n is an integer of 1 to 6.4. A photopolymerizable composition in accordance with claim 1, whereinsaid Ar¹ and Ar² are selected from the group consisting of phenyl andsubstituted phenyl groups.
 5. A photopolymerizable composition inaccordance with claim 1, wherein said Ar¹ and Ar² groups are selectedfrom the group consisting of thienyl and substituted thienyl groups. 6.A photopolymerizable composition in accordance with claim 4, wherein nis zero.
 7. A photopolymerizable composition in accordance with claim 4,wherein n is 1 and Z is a carbon-to-carbon bond.
 8. A photopolymerizablecomposition in accordance with claim 5, wherein n is zero.
 9. Aphotopolymerizable composition in accordance with claim 4, wherein Ar¹and Ar² are alkylphenyl groups.
 10. A photopolymerizable composition inaccordance with claim 1, wherein said halogen-containing complex anionis selected from the group consisting of tetrafluoroborate,hexafluorophosphate, and hexafluoroantimonate.
 11. A photopolymerizablecomposition in accordance with claim 1, wherein said photoinitiator ispresent in an amount of about 2 to 7 parts by weight per 100 parts byweight of said organic compound.
 12. A process for obtaining a curedcoating comprising:(a) applying a thin layer of the composition of claim1 to a substrate, and (b) exposing said layer to actinic radiation. 13.A substrate bearing a thin layer of the composition of claim 1 which hasbeen cured in situ by means of exposure to actinic radiation.
 14. Aprocess for bonding a radiation-transparent substrate to a secondsubstrate comprising:(a) disposing a layer of the composition of claim 1between said substrates and in contact therewith; and (b) exposing saidlayer to actinic radiation through said radiation-transparent substratein an amount and for a time sufficient to render said layer insoluble.15. A photopolymerizable composition comprising an admixture of:(a) 80to 100 parts by weight of a diglycidyl ether of Bisphenol A, (b) up to20 parts by weight of a phenyl glycidyl ether, (c) up to 10 parts byweight of a solvent carrier, (d) 0.5 to 20 parts by weight of anaromatic iodonium complex salt photoinitiator of the formula ##STR8##wherein Ar¹ and Ar² are aromatic groups having 4 to 20 carbon atoms andare selected from the group consisting of phenyl, thienyl, and furanylgroups; Z is an oxygen atom, a carbon-to-carbon bond, or ##STR9## whereR₁ and R₂ are selected from the group consisting of hydrogen, an alkylradical having 1 to 4 carbon atoms and an alkenyl radical having 2 to 4carbon atoms; n is zero or 1; and X⁻ is a halogen-containing complexanion selected from the group consisting of tetrafluoroborate,hexafluorophosphate, hexafluoroarsenate, hexachlorostannate andhexafluoroantimonate; and (e) 0.01 to about 1 part by weight of asensitizing dye per part of said photoinitiator.
 16. A visible lightcurable epoxy resin composition consisting essentially of by weight(a)an epoxy resin; (b) from 0.1% to 30% of (a) of a photoinitiatorconsisting essentially of an aryliodonium salt of the formula ##STR10##(c) from 0.005% to 30%, based on the weight of (a), of a cationic dyeselected from the class consisting of Acridine orange, Benzoflavin andSetoflavin T;wherein Ar¹ and Ar² are aromatic groups having 4 to 20carbon atoms and are selected from the group consisting of phenyl,thienyl, and furanyl groups; Z is an oxygen atom, a carbon-to-carbonbond, or ##STR11## where R₁ and R₂ are selected from the groupconsisting of hydrogen, an alkyl radical having 1 to 4 carbon atoms, andan alkenyl radical having 2 to 4 carbon atoms, and n is zero or 1; andX⁻ is a halogen-containing complex anion selected from the groupconsisting of tetrafluoroborate, hexafluorophosphate,hexafluoroarsenate, hexachloroantimonate, and hexafluoroantimonate. 17.A composition as in claim 16 where the photoinitiator isdiphenyliodonium hexafluorophosphate.
 18. A composition as in claim 16where the organic dye is acridine orange.